A storage pool is a collection of discs, redundant arrays of inexpensive discs (RAIDs), or other storage devices that have similar properties. A plurality of storage pools can be managed by a file system. A file system can be seen as a method for storing and organizing files and the data they contain on each storage pool of the plurality of storage pools so that the files and the data can be, e.g., retrieved from the storage pools.
A file system can manage and organize files on the storage pools by use of so called policies. A policy is a set of rules that specifies how a file is to be handled. For example, a so called placement policy could specify that all newly created files are to be placed to a first storage pool of the plurality of storage pools, wherein the first storage pool is the storage pool which provides the highest access rate of all storage pools of the plurality of storage pools. If a new file is created, then the new file is based on the above mentioned placement policy assigned to the first storage pool and all data written to the file is stored on the first storage pool.
Another so called management policy can further determine that newly created files are migrated from the first storage pool to a second storage pool of the plurality of storage pools if these files match to the criteria given by the policy e.g. are not accessed for the period of a month.
A hierarchical storage management (HSM) system can be further used to manage the file system associated with a plurality of storage pools. The hierarchical storage management system can for example be employed to monitor the filling level of the file system. The filling level of the file system refers to the relative amount of storage space occupied by the file system on the storage pools with respect to the total storage space provided by the plurality of storage pools.
If the HSM system detects for example that the filling level reaches an out of space condition (ENOSPACE) which corresponds to a filling level of 100%, the HSM system starts migrating the old and large files from the storage pools to a server system that is connected to the storage pools and substitutes the original files through a smaller stub file. A stub file is a very small file which is a pointer to the original file on the server. The storage system can for example provide cheap storage devices such as tapes so that the migrated data is stored in a cheap manner.
An individual storage pool of the plurality of storage pools might however reach the out of space condition long before the file system or correspondingly the plurality of storage pools reach the out of space condition. As the HSM system only controls the filling levels of the file system, it is not able to detect when an individual storage pool reaches the out of space condition. For example, if the first storage is full with data, the above mentioned placement policy does not work anymore, and in the worst case, when no default placement policy is defined, no new files that match to that placement policy can be created on the file system as there is no storage space available anymore on the first storage pool while there might still be lots of storage space available on the second storage pool keeping the filling level of the file system for away from the out of space condition.
There is therefore a need for an improved method and data processing system for controlling filling levels of each storage pool of a plurality of storage pools.